This invention is in the area of synthetic nucleosides, and is specifically directed to 1,3-oxaselenolane nucleosides and their pharmaceutical uses, compositions, and method of preparation.
In 1981, acquired immune deficiency syndrome (AIDS) was identified as a disease that severely compromises the human immune system, and that almost without exception led to death. In 1983, the etiological cause of AIDS was determined to be the human immunodeficiency virus (HIV).
In 1985, it was reported that the synthetic nucleoside 3xe2x80x2-azido-3xe2x80x2-deoxythymidine (AZT) inhibits the replication of human immunodeficiency virus. Since then, a number of other synthetic nucleosides, including 2xe2x80x2,3xe2x80x2-dideoxyinosine (DDI), 2xe2x80x2,3xe2x80x2-dideoxycytidine (DDC), 2xe2x80x2,3xe2x80x2-dideoxy-2xe2x80x2,3xe2x80x2-didehydrothymidine (D4T), and (1S,4R)-4-[2-amino-6-cyclopropyl-amino)-9H-purin-9-yl]-2-cyclopentene-1-methanol succinate (xe2x80x9c159U89xe2x80x9d), have been proven to be effective against HIV. In general, after cellular phosphorylation to the 5xe2x80x2-triphosphate by cellular kinases, these synthetic nucleosides are incorporated into a growing strand of viral DNA, causing chain termination due to the absence of the 3xe2x80x2-hydroxyl group. They can also or alternatively inhibit the viral enzyme reverse transcriptase or DNA polymerase.
The success of various synthetic nucleosides in inhibiting the replication of HIV in vivo or in vitro has led a number of researchers to design and test nucleosides that substitute a heteroatom for the carbon atom at the 3xe2x80x2-position of the nucleoside. Norbeck, et al., disclosed that (xc2x1)-1-[(2xcex2,4xcex2)-2-(hycroxymethyl)-4-dioxolanyl]thymine (referred to as (xc2x1)-dioxolane-T) exhibits a modest activity against HIV (EC50 of 20 xcexcM in ATH8 cells), and is not toxic to uninfected control cells at a concentration of 200 xcexcM. Tetrahedron Letters 30 (46), 6246, (1989). European Patent Application Publication No. 0 337 713 and U.S. Pat. No. 5,041,449, assigned to BioChem Pharma, Inc., disclose racemic 2-substituted-4-substituted-1,3-dioxolanes that exhibit antiviral activity. Published PCT applications PCT/US91/09124 and PCT/US93/08044 disclose purified xcex2-D-1,3-dioxolanyl nucleosides for the treatment of HIV infection. PCT discloses the use of purified xcex2-D-1,3-dioxolanyl nucleosides for the treatment of HBV infection.
PCT/US95/11464 discloses that (xe2x88x92)-(2S,4S)-1-(2-hydroxymethyl-1,3-dioxolan-4-yl)cytosine is useful in the treatment of tumors and other abnormal cell proliferation.
U.S. Pat. No. 5,047,407 and European Pat. Application Publication No. 0 382 526, both to BioChem Pharma, Inc., disclose that a number of racemic 2-substituted-5-substituted-1,3-oxathiolane nucleosides have antiviral activity, and specifically report that the racemic mixture of 2-hydroxymethyl-5-(cytosin-1-yl)-1,3-oxathiolane (referred to below as BCH-189) has approximately the same activity against HIV as AZT, with less toxicity. U.S. Pat. No. 5,539,116 to Liotta, et al is directed to the (xe2x88x92)-enantiomer of BCH-189, known as 3TC, is now sold commercially for the treatment of HIV in humans in the United States.
It has also been disclosed that cis-2-hydroxymethyl-5-(5-fluorocytosin-1-yl)-1,3-oxathiolane (xe2x80x9cFTCxe2x80x9d) has potent HIV activity. Schinazi, et al., xe2x80x9cSelective Inhibition of Human Immunodeficiency viruses by Racemates and Enantiomers of cis-5-Fluoro-1-[2-(Hydroxymethyl)-1,3-Oxathiolane-5-yl]Cytosinexe2x80x9d Antimicrobial Agents and Chemotherapy, November 1992, page 2423-2431. See also U.S. Pat. Nos. 5,210,085; 5,204,466, WO 91/11186, and WO 92/14743.
Another virus that causes a serious human health problem is the hepatitis B virus (referred to below as xe2x80x9cHBVxe2x80x9d). HBV is second only to tobacco as a cause of human cancer. The mechanism by which HBV induces cancer is unknown. It is postulated that it may directly trigger tumor development, or indirectly trigger tumor development through chronic inflammation, cirrhosis, and cell regeneration associated with the infection.
After a two to six month incubation period in which the host is unaware of the infection, HBV infection can lead to acute hepatitis and liver damage, that causes abdominal pain, jaundice, and elevated blood levels of certain enzymes. HBV can cause fulminant hepatitis, a rapidly progressive, often fatal form of the disease in which massive sections of the liver are destroyed.
Patients typically recover from acute hepatitis. In some patients, however, high levels of viral antigen persist in the blood for an extended, or indefinite, period, causing a chronic infection. Chronic infections can lead to chronic persistent hepatitis. Patients infected with chronic persistent HBV are most common in developing countries. By mid-1991, there were approximately 225 million chronic carriers of HBV in Asia alone, and worldwide, almost 300 million carriers. Chronic persistent hepatitis can cause fatigue, cirrhosis of the liver, and hepatocellular carcinoma, a primary liver cancer.
In western industrialized coutrines, high risk groups for HBV infection include those in contact with HBV carriers or their blood samples. The epidemiology of HBV is very similar to that of acquired immune deficiency syndrome, which accounts for why HBV infection is common among patients with AIDS or AIDS related complex. However, HBV is more contagious than HIV.
Both FTC and 3TC exhibit activity against HBV. See Furman, et al., xe2x80x9cThe Anti-Hepatitis B Virus Activities, Cytotoxicities, and Anabolic Profiles of the (xe2x88x92) and (+) Enantiomers of cis-5-Fluoro-1-[2-(Hydroxymethyl)-1,3-oxathiolane-5-yl]-Cytosinexe2x80x9d Antimicrobial Agents and Chemotherapy, December 1992, page 2686-2692; and Cheng, et al., Journal of Biological Chemistry, Volume 267(20), 13938-13942 (1992).
A human serum-derived vaccine has been developed to immunize patients against HBV. However, more recently, vaccines have also been produced through genetic engineering and are currently used widely. Unfortunately, vaccines cannot help those already infected with HBV. Daily treatment with xcex1-interferon, a genetically engineered protein, has also shown promise, but this therapy is only successful in about one third of treated patients. Further, interferon cannot be given orally.
Since 1,3-doxolane and 1,3-oxathiolane nucleosides have exhibited promising antiviral and anticancer activities, it was of interest to synthesize an isosteric class of compounds, 1,3-oxaselenolane nucleosides in search of biologically interesting nucleosides. Despite their structural similarity to the 3xe2x80x2-heteroatom substituted nucleosides, the synthesis of 1,3-oxaselenolane nucleosides has been elusive as the construction of the oxaselenolane ring is difficult. For this reason, it appears that 1,3-oxaselenolane nucleosides have never been reported.
In light of the fact that acquired immune deficiency syndrome, AIDS-related complex, and hepatitis B virus have reached epidemic levels worldwide, and have tragic effects on the infected patient, there remains a strong need to provide new effective pharmaceutical agents to treat these diseases.
Therefore, it is an object of the present invention to provide a method and composition for the treatment of human patients infected with HIV.
It is another object of the present invention to provide a method and composition for the treatment of human patients or other host animals infected with HBV.
It is a further object of the invention to provide a method for the synthesis of 1,3-oxaselenolanyl nucleosides.
It is a still further object of the invention to provide 1,3-oxaselenolanyl nucleosides and pharmaceutical compositions that include 1,3-oxaselenolanyl nucleosides.
A method and composition for the treatment of HIV or HBV infection in humans and other host animals is disclosed that includes the administration of an effective amount of a 1,3-oxaselenolane nucleoside or a pharmaceutically acceptable salt thereof, optionally in a pharmaceutically acceptable carrier.
In one embodiment, the 1,3-oxaselenolane nucleoside has the formula: 
wherein B is a purine or pyrimidine base, and R is hydrogen, acyl or a phosphate ester, including monophosphate, diphosphate, or triphosphate. In another embodiment, the 1,3-oxaselenolanyl nucleoside is provided as a lipophilic or hydrophilic prodrug as discussed in more detail below. In another alternative embodiment, the selenium atom is oxidized in the molecule. Preferred 1,3-oxaselenolanyl nucleosides are those that exhibit an activity against HIV or HBV at a concentration of not greater than approximately 5 micromolar, and most preferably approximately 1 micromolar or less in an in vitro assay such as those described in detail in this application. For treatment of HIV and HBV, it is also preferred that the 1,3-oxaselenolanyl nucleoside exhibit an IC50 toxicity in an in vitro assay such as those described herein of greater than 50 micromolar, and more preferably, approximately 100 micromolar or greater.
The 1,3-oxaselenolane nucleoside is preferably either a xcex2-L-nucleoside or a xcex2-D-nucleoside, as an isolated enantiomer. In one embodiment, the nucleoside is a xcex2-L- or xcex2-D-nucleoside in substantially pure form, i.e., substantially in the absence of the corresponding xcex2-D- or xcex2-L-nucleoside.
Preferred compounds are 2-hydroxymethyl-4-(N-5xe2x80x2-cytosin-1xe2x80x2-yl)-1,3-oxaselenolane and 2-hydroxymethyl-4-(N-5xe2x80x2-fluorocytosin-1xe2x80x2-yl)-1,3-oxaselenolane. It has been discovered that the isolated (xe2x88x92)-xcex2-L-enantiomer of these nucleosides are more potent than their xcex2-D counterparts. The (+)-enantiomers of these compounds, however, are not toxic to CEM cells.
In another embodiment, the active compound or its derivative or salt can be administered in combination or alternation with another antiviral agent, such as an other anti-HIV agent or anti-HBV agent, as described in more detail in Section IV. In general, during alternation therapy, an effective dosage of each agent is administered serially, whereas in combination therapy, an effective dosage of two or more agents are administered together. The dosages will depend on absorption, inactivation, and excretion rates of the drug as well as other factors known to those of skill in the art. It is to be noted that dosage values will also vary with the severity of the condition to be alleviated. It is to be farther understood that for any particular subject, specific dosage regimens and schedules should be adjusted over time according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions.
The compounds can also be used to treat equine infectious anemia virus (EIAV), feline immunodeficiency virus, and simian immunodeficiency virus. (Wang, S., Montelaro, R., Schinazi, R. R., Jagerski, B. and Mellors, J. W.: Activity of nucleoside and non-nucleoside reverse transcriptase inhibitors (NNRTI) against equine infectious anemia virus (EIAV). First National Conference on Human Retroviruses and Related Infections, Washington, D.C., Dec. 12-16, 1993; Sellon D. C., Equine Infectious Anemia, Vet Clin. North Am. Equine Pract. United States, 9: 321-336, 1993; Philpott, M. S., Ebner, J. P., Hoover, E. A., Evaluation of 9-(2-phosphonylmethoxyethyl)adenine therapy for feline immunnodeficiency virus using a quantitative polymerase chain reaction, Vet. Inumunol. Immunopathol. 35:155166, 1992.)